Generally speaking, the use of beam shaping electrodes in CRT electron guns to beneficially modify the lensing of the beams is known in the art. Discrete beam shapings minimize deflected spot distortion, such being especially true when self converging yokes are employed with in-line gun tubes. Electrodes with beam shaping properties provide a lensing field of equipotential lines of force to form the bundle of moving electrons into a beam of desired cross-sectional shaping. Exemplary art is evidenced in U.S. Pat. Nos. 3,852,608, 3,866,081 and 4,143,293. Such prior art techniques are complicated and expensive to fabricate, and require either a multiple part electrode or cooperation between two or more electrodes.
Some beam shaping electrodes have been manufactured as two-piece structures in an effort to achieve the desired beam forming characteristics. For example, the prior art discloses beam shaping electrodes constructed of two superimposed rectangularly slotted elements affixed in orthogonal relationship to provide a substantially square aperture therethrough. In fabrication, it is difficult to keep proper alignment between the two slots, and the affixural welding can produce surface imperfections which are deleterious to the forming of the desired beam shaping lensing.
Attention is also directed to three previously and concurrently filed patent applications which are assigned to the assignee of the present invention. These applications are Ser. No. 94,405, now U.S. Pat. No. 4,307,498, 94,409, now U.S. Pat. No. 4,272,700, and 94,515, now U.S. Pat. No. 4,251,747, all of which were filed Nov. 15, 1979. The respective disclosures in these applications relate to the field of the present invention, but differ markedly therefrom.